Frequency to voltage converters receive an alternating electrical input signal having a frequency, and provide an analog output voltage that is proportional to the frequency of the electrical input signal.
Some frequency to voltage converters are based on sample and hold mechanisms in which a capacitor is charged during a charging phase. With a sample and hold frequency to voltage converters the higher the frequency becomes, the less the capacitor charges resulting in a corresponding decreasing output voltage. The output voltage may also be linearly correlated with a charging current, which can be voltage and temperature dependent. Parasitic capacitance noise generated by the sampling mechanism may also be linearly correlated with the output voltage.
Thus, neither of these approaches is suitable for high accuracy clock designs.